A vehicle alternator mounted to the engine of a vehicle is often splashed with water and in particular with muddy water when it is actually used. On the other hand, a vent hole is disposed to the rear bracket as the casing of the alternator to radiate the heat generated by the generation of power. It is preferable that the vent hole is made as large as possible to improve a heat radiating property. Since, however, the vent hole cannot be made large from the view point of the role of the rear bracket for protecting the components accommodated therein and the necessity for securing the strength of the rear bracket itself, a plurality of the vent holes each having a proper size are disposed. Such being the case, in the conventional alternator, since water such as muddy water and the like is liable to come into it through the vent holes, the alternator is provided with a water discharge hole disposed to the lower side of the rear bracket to thereby effectively discharge water coming into it.
FIG. 7 is a front elevational view of a rear bracket applied to a conventional alternator.
In FIG. 7, the rear bracket 1 of the alternator has a plurality of vent holes la each having a proper size and disposed thereto. A water discharge hole 1b is disposed to the lower side of the rear bracket 1. The water discharge hole 1b is formed by cutting out the wall surface of the terminal mounting portion 1c of the rear bracket 1 as shown in FIG. 8.
As shown in FIG. 9, the rear bracket 1 is disposed coaxially with a stator core 2 and journals a rotary shaft 3 driven by an engine 11 at the rear end thereof. A rectifier 4 is mounted to the terminal mounting portion 1c of the rear bracket 1.
As shown in FIG. 11, the alternator 10 arranged as described above is mounted to the engine 11 so that the main surface of the rear bracket 1 faces in a vertical direction. The terminal mounting portion 1c is located on a lower side (ground side) and the opening of the water discharge hole 1b faces downward.
When the alternator 10 is splashed with water 5 such as muddy water and the like, the water 5 comes into the alternator 10 from the vent holes 1a. The water 5 having come into the alternator 10 flows along the inside wall surface of the rear bracket 1 and is discharged from the water discharge hole 1b to the outside.
In, for example, the terminal mounting portion 1c to which the rectifier 4 is mounted, the interval between the inside wall surface of the rear bracket 1 and the rectifier 4 is narrowed. Thus, when the water 5 comes into the terminal mounting portion 1c arranged as described above, the water 5 is deposited on the rectifier 4 by surface tension as shown in FIG. 10 and difficult to be discharged from the water discharge hole lb. When the water 5 contains many types of impurities such as mud and the like, they are dried without being discharged from the water discharge hole 1b and clog the water discharge hole 1b by the repetition of the above process. When the water discharge hole 1b is clogged, since the water 5 having come into the alternator 10 stays there without being discharged, there is a problem that the water makes the components accommodated in the rear bracket 1 such as the rectifier 4 and the like to an unacceptable state and causes a voltage drop by the contact of the rear bracket I serving as the ground with the components, whereby a breakdown is arisen.